Membrane filters of various polymeric materials are known and are generally thin porous structures having porosities between about 50-80% by volume. They are relatively fragile and are commonly used with various types of mechanical support or reinforcement. Flow rates of liquids through such membranes per unit of area are a function of pore size. To obtain high flow rates through filters with fine pores, for example below about one micron, relatively large filter areas are needed. Such areas have therefore been provided by using large individual filters or by using a number of smaller individual filters in parallel. For use in critical pharmaceutical applications such as sterilization, such membranes and their supporting apparatus must be free of leaks or defects capable of passing small particles or organisms.
Numbers of small filters have theretofore been hand-assembled for parallel flow with supporting plates and associated apparatus, then tested, and, if necessary, sterilized, often at the user's site at considerable cost and inconvenience. The operations must be repeated if the hand assembly fails the necessary tests. The mechanical parts of larger more complex filtration systems are generally cleaned and re-used with only the filters being replaced. One assembly heretofore provided in disposable plastic has also been mechanically secured with relatively moveable parts.
Individual membrane filters of large area have been supported flat or cylindrically, or have been pleated for disposition in compact housings. Holders for flat membranes are large, for a given filter area, are usually not disposable, and also require disassembly, cleaning, reassembly and testing with each change of filter. Pleating of fragile membranes creates stress concentrations at the folds, permits flexing of the fragile membranes in use, normally requires interleaving flow screens on one or both of the upstream and downstream sides and requires potting and/or adhesives to seal the ends and overlapping seams. Because of concerns for possible failures at the folds, seams, or ends, a separate flat final filter is sometimes used in series with pleated cartridges for added assurance in critical applications, for example, in sterilizing pharmaceuticals and intravenous fluids. In addition, the use of a number of different materials in pleated cartridge construction increases the sources for extractibles into the filtrate.
The fluid processed in presently available filter cartridges experiences pressure drop which limits the volume of fluid that can be processed through the cartridge. The degree of pressure drop is closely related to the flow path length of the fluid within the cartridge. The longer the flow path length, the greater the pressure drop.
U.S. Pat. No. 4,501,663 discloses a filtration cartridge formed from a plurality of stacked filtration modules and having a separate exterior housing. The cartridge is undesirable since it has a large hold up volume which results in sample loss.
U.S. patent application Ser. No. 60/925,774, filed Apr. 23, 2007 discloses a filtration cartridge having a feed inlet and a permeate outlet positioned at a central portion of the cartridge. This cartridge requires a fluid deflection plate to direct incoming fluid feed from a central portion of the cartridge to a peripheral portion of the cartridge. The inclusion of a deflection plate is undesirable since it adds a nonworking element to the cartridge.
At the present time an integrity test utilizes a binary gas for determining the presence of defects in membranes in a filtration cartridge. The test provides greater accuracy when the binary gas is flowed in a tangential flow filtration mode (TFF) rather than a normal flow filtration mode (NFF) (dead ended filtration). This integrity test is described in U.S. patent application Ser. No. 11/545,738, filed Oct. 10, 2006 which is incorporated herein by reference. Accordingly, when it is desired to effect NFF filtration within a filtration cartridge and to effect the integrity test, the filtration cartridge must be capable of being operated in both TFF and NFF modes.
Accordingly, it would be desirable to provide a filtration cartridge having a single feed inlet and a single permeate outlet for reasons of simplicity. In addition, it would be desirable to provide such a cartridge which can be operated in both TFF and NFF modes. Furthermore, it would be desirable to provide a filtration cartridge with a minimum of nonworking elements to reduce cost. In addition, it would be desirable to provide such a cartridge wherein the fluid being processed experiences a low pressure drop within the cartridge as compared to presently available cartridges.